54 THE RESTING AND DIVIDING CELL 



called the reticular theory. A second group of scientists believes 

 that protoplasm is similar to a mass of bubbles, like soapsuds or a 

 froth. This group thinks the so-called fibers are only the delicate 



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The structure of protoplasm has not been satisfactorily determined. It has been described in 

 various ways and represented as in the above diagrams. 



lines separating the bubbles from each other. This theory is called 

 the alveolar or the foam theory. A third group thinks that proto- 

 plasm is an infinite number of very small, living, moving granules 

 arranged in lines resembling fibers. These fibers, differently ar- 

 ranged, make various figures This is the granular theory. All 

 biological problems are centered in the cell, including the manu- 

 facture and use of food, and an understanding of the nature of 

 and the control of problems of heredity. Such problems shall 

 never be satisfactorily settled until more knowledge of the work 

 of the cell is gained. 



Many investigators are now trying to solve cell problems. Con- 

 sider the work of Alexis Carrell, the French surgeon. For years 

 he and his assistants have been working at Rockefeller Institute, 

 New York city, trying to develop various cells outside of a living 

 organism. For sixteen years he has kept cells of a chicken embryo 

 actively growing. He has also succeeded in getting other living 

 cells to grow under controlled circumstances. He has been able to 

 use some of these cultivated cells to try out the effects of various 

 antiseptics. It is possible that cultivated tissues will be of great 

 value in operations of skin grafting. Growing tissues for this 

 purpose is only one small part of the work now being done by 

 Carrell. He has transplanted whole organs from one animal to 



